The long-term goal of this project is to obtain information required to elucidate the mechanism by which Na, K ions - ATPase, the in vitro manifestation of the sodium pump, couples the hydrolysis of ATP to transport of sodium and potassium against their concentration gradients and the mechanism by which cardiac glycosides interact with Na, K ions -ATPase to inhibit its activity. Another objective of this project is to ascertain the mechanism by which cardiac glycosides cause an increase in contractility of the heart. (RB)